1. Field of the Invention
This application relates to wireless systems and more particular to wireless systems using closed loop transmit diversity.
2. Description of the Related Art
In recent years, multiple transmit antenna techniques have been widely studied to improve the capacity of wireless systems. In fact, current Wireless LAN (WLAN) standards (such as the IEEE 802.11n) deploy multiple antennas to transmit at either the base station and/or the client station. This approach increases the capacity of the wireless link and provides significant diversity gain. Streaming applications, such as Voice over Internet Protocol (VoIP) telephony, entertainment audio and video, and conferencing are natural extensions of modern Ethernet's ability to combine real-time and data traffic on a common system, thus lowering costs and providing inter-application service synergies. These real-time applications, however, are less forgiving of late packet delivery, either due to back-off resulting from system loading, or retransmission delays arising from contention, channel imperfection and consequent contention resolution (CR). Although the bounding of latency and jitter consistent with high-quality delivery of multimedia services can be achieved with wired LANs using switched-Ethernet or higher transmission rates, these are harder to apply with wireless Ethernets.
Multiple antenna systems have been broadly adopted in wireless communications to increase system capacity and improve performance. To achieve high spatial efficiency and reliability, transmit/receive diversity techniques have been considered. One such approach is Protocol Assisted Switched Diversity (PASD), which is an error control technique that utilizes Media Access Control (MAC) protocol elements and companion signal processing with multiple antennas and a single radio at the receiver to provide improved Quality of Service (QoS) performance with current IEEE 802.11 radio chipsets. The approach is described in U.S. Publication Number 20030096617, published May 22, 2003.